1. Technical Field
The present invention relates to an electric power applying circuit for supplying power to a load, and a test apparatus for testing a device under test (DUT). More particularly, the present invention relates to an electric power applying circuit for supplying a direct current (DC) power to a load and a test apparatus for conducting a DC test on a DUT.
2. Related Art
It is known that a device under test (DUT) such as a semiconductor circuit is tested by way of direct current (DC) tests according to which, for example, a voltage is applied and a resultant current is measured, and a current is applied and a resultant voltage is measured. In the case of a test in which a voltage is applied and a resultant current is measured, for example, while applying a predetermined DC voltage to the DUT, a test apparatus detects a DC current flowing within the DUT when the DUT is operating or not operating. When the detected DC current does not fall within a predetermined range, the test apparatus judges the DUT to be defective.
A conventionally known circuit for supplying a DC power to a DUT is constituted by using an amplifier, for example, as disclosed in Unexamined Japanese Patent Application Publication No. H05-119110. The amplifier amplifies an input voltage, and applies the amplified voltage to the DUT.
To apply, to the DUT, a voltage whose voltage value is high and highly accurately controlled, the circuit needs to be constituted by using a high-accuracy and high-voltage amplifier. Such an amplifier is expensive, thereby increasing the cost of the circuit.
As disclosed in Patent Document 1, for example, a voltage-applying/current-measuring circuit is known which applies a constant voltage to a DUT and measures a current supplied to the DUT. When the voltage-applying/current-measuring circuit applies a high voltage to the DUT, each of the elements constituting the circuit needs to be formed by using a high-accuracy and high-voltage element.
Even when a floating power source is used to supply power source voltages to some of the elements constituting the circuit as disclosed in FIG. 1 of Patent Document 1, constituents such as a main amplifier 13, a differential amplifier 21, and a resistor 25 need to be configured by using high-accuracy and high-voltage elements. This increases the cost of the circuit. Furthermore, since the floating power source is used for some of the elements constituting the circuit, the circuit has a complex configuration, which also contributes to an increase in the cost of the circuit.
In view of the above, an advantage of some embodiments of the present invention is to provide an electric power applying circuit and a test apparatus which can solve the above-described problems. This advantage is achieved by combining the features recited in the independent claims. The dependent claims define further effective specific example of the present invention.